The system provides for one or more photovoltaic panels (3) or other energy sources, connected to a series of inverters (5) in parallel, the outputs of which are connected to a load (Z) and/or to an electricity distribution grid (7). One of the inverters operates as master unit and generates a power control signal in order to track the maximum power point that can be obtained from the panels (3). The other inverters operate as slave units. The control is performed so that all the inverters absorb a variable quantity of power according to the fluctuations in the power available at the output of the photovoltaic panels (3) or other source subject to fluctuations.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for managing a system for generation of electric power, the system including at least one direct current (DC) source which delivers at a DC source output an electric power subject to fluctuations, and a plurality of inverters comprising a respective control unit and having a respective inverter output and a respective inverter input connected to said DC source output, and wherein each of the inverters is functional to transform the electric power at the inverter input into ac electric power at the inverter output with controlled frequency and voltage, the method comprising the steps of: selecting one of said inverters as a master unit and the remaining inverters as slave units; performing, via said master unit, a maximum power point tracking algorithm to generate a power modulation control signal via said master unit; and using said power modulation control signal to concurrently control and manage in parallel the master unit and at least an active one of the slave units to vary the power absorbed by said master unit and by said at least one active slave unit, so that each of said master unit and said at least one active slave unit delivers a variable power output that tracks the fluctuations of the power at the output of said direct current source by tracking a maximum power point via the maximum power point tracking algorithm performed by said master unit.
2. The method of claim 1 , wherein said master unit and each of said slave units are controlled to each deliver substantially the same output power, said output power varying according to the power delivered by said direct current source.
3. The method of claim 2 , wherein said power modulation control signal is effective to cause the voltage at the input of each of said master unit and said slave units to fluctuate around a value that maximizes the power delivered by said direct current source, simultaneously varying the power delivered by said master unit and said slave units via said power modulation control signal.
4. The method of claim 3 , wherein said direct current source comprises at least one photovoltaic panel.
5. The method of claim 4 , wherein said master unit performs said maximum power point tracking algorithm by cyclically perturbing the voltage at the direct current power source output and monitoring a variation in power delivered by said direct current source resulting from said perturbation, and said master unit generates the power modulation control signal for the power at the output of said master unit and said slave units such as to maintain the output voltage of said direct current source around the point of maximum power delivered by said source when an external parameter varies.
6. The method of claim 5 , wherein said external parameter comprises a power per surface unit collected by said at least one photovoltaic panel.
7. The method of claim 6 , wherein the power delivered by said inverters is controlled by controlling a phase displacement between voltage and current at the output of the inverters.
8. The method of claim 7 wherein one of said inverters is selected as master unit at a start-up of said system.
9. The method of claim 8 , wherein one of said inverters is selected as master unit at each start-up of said system.
10. The method of claim 8 wherein at a start-up of said system, each inverter generates a respective random number and the master unit is selected on the basis of the random numbers generated by said inverters.
11. The method of claim 10 wherein the inverter that generates the highest random number is selected as the master unit.
12. The method of claim 10 , wherein the inverter that generates the lowest random number is selected as the master unit.
13. The method of claim 1 wherein the power delivered by at least one of said inverters is varied so as to maintain said power around a maximum efficiency point of the inverter.
14. The method of claim 1 further comprising providing two inverters and modulating the power modulation control signal for the power delivered by each of said inverters so as to maximize the efficiency of said inverters.
15. The method of claim 1 wherein each of the inverters is coupled to said DC source, the method further comprising varying the power delivered by each of said inverters by means of said power modulation control signal generated by the master unit.
16. The method of claim 1 wherein the number of inverters connected in parallel at the output of said direct current source is varied over time to minimize the number of inverters active and to optimize the efficiency of each inverter, according to the theoretical maximum power that can be delivered by said DC source as a function of time.
17. An electric power DC/AC conversion system, comprising: a plurality of inverters configured to be connected in parallel and each inverter comprising an inverter input, an inverter output and a respective control unit, wherein: each of said inverters is functional to receive at the respective inverter input a dc electric power subject to fluctuations and for delivering an ac power with controlled frequency and voltage at the respective inverter output; one of said inverters is defined as a master unit, and each of the other inverters is defined as a slave unit; said master unit is effective to perform a maximum power point tracking algorithm on the direct current fluctuating at the input of said inverters, and generate a power modulation control signal for each of said inverters; and each of said control units is configured to concurrently control and manage in parallel at least an active one of said slave units and the master unit according to said power modulation control signal so that said master unit and said at least one active slave unit each deliver a variable power that tracks the fluctuations of the power at the output of said direct current source by tracking the maximum power point via the maximum power point tracking algorithm performed by said master unit to thereby provide at the inverter output of each of said master and slave units an ac power which is variable and modulated according to the fluctuating input power.
18. The system of claim 17 wherein each of the control units of said master unit and said slave units are configured to cause each of said master unit and said slave units to substantially deliver the same output power, said output power varying according to the input power.
19. The system of claim 18 further comprising a dc power source, the dc power source having an output coupled to the respective inverter inputs of each of said inverters.
20. The system of claim 19 , wherein said dc power source comprises at least one photovoltaic panel.
21. The system of claim 20 wherein said power modulation control signal is effective to cause the voltage at the input of said master unit and said slave units to fluctuate around a value that maximizes the power delivered by said direct current source, simultaneously varying the power delivered by said master unit and said slave units using said power modulation control signal.
22. The system of claim 21 wherein each of the control units is configured to cause said master unit to perform said maximum power point tracking algorithm by cyclically perturbing the voltage at the output of the dc power source and observing the variation in power delivered by said direct current source resulting from said perturbation, and generating a power modulation control signal at the output of said master unit and said slave units such as to maintain the output voltage of said direct current source around the point of maximum power delivered by the source when an external parameter varies.
23. The system of claim 22 wherein said external parameter comprises a power per surface unit collected by said at least one photovoltaic panel.
24. The system of claim 23 wherein each of said control units is further configured to control the power delivered by said inverters by acting on the phase displacement between voltage and current at the inverter output of the inverters.
25. The system of claim 24 wherein each of said inverters is coupled to said direct current power source without the interposition of switching devices.
26. The system of claim 17 wherein each of said control units is further configured to select of one of said inverters as the master unit and the other inverters as slave units.
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June 6, 2007
January 7, 2014
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